What is the ruling on a father getting angry at his son for no reason and secretly supplicating against him with cancer?

The rights of parents are immense, and Allah has commanded kindness and dutifulness towards them. Allah Almighty says: (And We have enjoined upon man, to his parents, good treatment) and (and to parents, good treatment). The most beloved deeds to Allah after prayer are dutifulness to parents, then jihad. One must strive to be dutiful to their parents and be patient with any difficulties or harshness they may encounter.

If a parent becomes angry with their child without any fault on the child's part, then there is no sin upon the child. However, the child should strive to appease the parent and be gentle with them.

As for a parent supplicating against their child unjustly, it is impermissible; as the Prophet, peace and blessings be upon him, said: "Do not supplicate against yourselves, nor supplicate against your children, nor supplicate against your wealth." Some interpret that a parent's answered supplication against their child might be specific to cases of the child's disbelief or extreme disobedience.